Wickland turned away from conventional medical psychology and toward the belief that psychiatric illnesses were the result of influence by spirits of the dead.

Wickland came to believe that a large number of his patients had become possessedby what he called "obsessing spirits", and that low-voltage electric shocks could dislodge them, while his wife Anna acted as a medium to guide them to "progress in the spirit world".

Spiritualists considered him an authority on "destructive spirits" and he wrote a book in 1924, Thirty Years Among the Dead, detailing his experiences as a psychical researcher.

Wickland was convinced that he was in contact with a group of spirits known as the "Mercy Band" who would remove the possessors, and help them in the spirit world.